Upgrading Dovecot v2.0 to v2.1

v2.1 is mostly compatible with v2.0 configuration, except:

15-mailboxes.conf included in the default configuration now specifies a few default SPECIAL-USE mailboxes. This file assumes that you already have namespace inbox { .. } specified (in 10-mail.conf). If you don't, you'll get errors about namespaces. Note that the namespace's name must be "inbox" (as well as usually include inbox=yes setting). The solution is to either make sure that you have such a namespace defined, or you can simply delete the 15-mailboxes.conf if you don't care about SPECIAL-USE.

Solr full text search backend changed to use mailbox GUIDs instead of mailbox names, requiring reindexing everything. solr_old backend can be used with old indexes to avoid reindexing, but it doesn't support some newer features.

dsync was merged into doveadm. There is still "dsync" symlink pointing to "doveadm", which you can use the old way for now. The preferred ways to run dsync are "doveadm sync" (for old "dsync mirror") and "doveadm backup".

dsync protocol isn't compatible with v2.0's dsync, so you can't dsync between v2.0 and v2.1 servers.